Efeitos de doses de molibdênio aplicadas na folhagem na produtividade e conteúdo de molibdênio na semente de feijão-caupi

Abstract

Soils in Maranhão are generally sandy and acidic, conditions that favor the occurrence of plant nutrient deficiencies, particularly of phosphorus, nitrogen (N), and molybdenum (Mo). Consequently, cowpea grain yield in Maranhão is low relative to its productive potential. Adequate Mo supply to legumes reduces N deficiencies and the need for top-dressed mineral N fertilization. Therefore, our objective was to determine—under low-technology conditions in northern Maranhão—the foliar Mo rate applied at the cowpea V4 stage that maximizes yield, as well as the Mo rate required to raise seed Mo content to approximately 3.6 µg per seed (the level required for the crop in Minas Gerais). Field trials were conducted in 2022 in São Luís and Nina Rodrigues, Maranhão. No chemical fertilizer was applied at planting. Treatments were arranged in a 5 x 2 factorial design: foliar Mo rates applied at 25 days after emergence (DAE) in São Luís and 27 DAE in Nina Rodrigues (0, 50, 100, 200, or 300 g ha⁻¹) and top-dressed N rates (0 and 50 kg ha⁻¹). The cultivar BRS Guariba was used. The average number of nodules per plant was 6.5 in São Luís and 5.0 in Nina Rodrigues, and average yields were 465 kg ha⁻¹ in São Luís and 822 kg ha⁻¹ in Nina Rodrigues. In the absence of N, a foliar spray of 50 g ha⁻¹ of Mo increased leaf N content by 14.8% and grain yield by 50% compared to the zero-rate treatment. With N, Mo rates did not significantly influence these variables. There was no significant interaction between Mo rates and N rates regarding seed Mo content. However, the effect of the Mo rate factor on seed Mo content was highly significant. Foliar Mo applications increased seed Mo content by 140% to 614%. A seed Mo content of 3.54 µg was obtained with the 50 g ha⁻¹ Mo rate. Our results suggest that, for low-input cowpea cultivation, a foliar application of 50 g ha⁻¹ Mo is sufficient to maximize grain yield and produce Mo-enriched seeds.